Electromagnetic sensor for use in measurements on a subject

ABSTRACT

A sensor unit for use in measurements on a subject is presented. The sensor unit includes a near field electromagnetic sensor and a flexible signal transmission structure, which are integral with one another by means of at least one common continuous surface. The flexible signal transmission structure is constructed from a first layer including signal connection lines associated with sensor cells near field electromagnetic sensor and a second electrically conductive layer electrically coupled to the electrically conductive material of the sensor.

FIELD OF THE INVENTION

This invention is generally in the field of medical devices, and relatesto a tissue characterization sensor unit for use in measurements on asubject.

BACKGROUND OF THE INVENTION

Electromagnetic (EM) tissue characterization is a well known techniquethat utilizes an EM sensor to induce EM fields, of various frequencyranges, for example: constant (DC), low frequency, intermediatefrequency, high frequency, radio frequency (RF) and microwave (MW)range, within a tissue and to receive therefrom EM response indicativeof certain properties (e.g. dielectric properties) of the tissue portionlocated within a measurement region. The induced EM fields within thetissue may be near fields, or radiating fields. The EM response of thetissue might be characterized by certain EM resonance frequenciesassociated with the sensor-tissue coupling, or alternatively may be abroad band EM response (non-resonating) associated with thesensor-tissue coupling. Generally, the response of the tissue (or othermedium/substance as the case may be) to EM fields is associated with thedielectric properties of the tissue, the response being characterizedby, for example, absorbance, reflectance and/or transmittance of EMfields of different frequencies. Detection and analysis of the EMresponse of the tissue provides for differentiating between differenttissue types.

Typically, EM tissue characterization sensors are configured as aspatial configuration of conductors that are connected with signaltransmission lines, configured for carrying EM signals from anelectromagnetic signal generator to the tissue to be characterized, andfor carrying EM signals back from the tissue to be characterized to asignal analyzer.

For example, U.S. Pat. No. 6,813,515, assigned to the assignee of thepresent application, describes a probe, method and system for examiningtissue, in order to differentiate it from other tissues, according toits dielectric properties. The method is of generating an electricalfringe field in the examined tissue to produce a reflected pulsetherefrom with negligible radiation penetrating into the tissue itself;detecting the reflected electrical pulse; and comparing electricalcharacteristics of the reflected electrical pulse with respect to theapplied electrical pulse to provide an indication of the dielectricproperties of the examined tissue. The measuring device is built as acoaxial probe with cavity at its distal tip with respect to operatorwhere a sample of the tissue to be examined is confined. The probeitself has an inner conductor insulated from, and enclosed by, an outerconductor open at one end and extending past the inner conductor in theaxial direction, defining an open cavity at the distal end of the probewith respect to the operator. The inner conductor includes a tip withinthe open cavity, which tip is formed with at least two differentdiameters for enhancing the electrical fringe field.

Some other examples of the tissue characterization sensors are describedin the patent publications: U.S. Pat. No. 6,380,747; U.S. Pat. No.5,227,730; U.S. Pat. No. 5,334,941; U.S. Pat. No. 6,411,103. Also, somesensors are exemplified in WO 06/103665 assigned to the assignee of thepresent application.

The use of an arrangement of multiple tissue characterization sensors isdescribed for example in US 2008/0200803. Here, a cancer detection andtreatment instrument is described. The instrument comprises: a firstconductive plate; a second conductive plate which is opposed to thefirst conductive plate and has a first opening; a first signal linedisposed between the first conductive plate and the second conductiveplate; a first contact member of which one end is exposed through thefirst opening and of which the other end is connected to the firstsignal line; a dielectric portion filled between the first and secondconductive plates and the first signal line; and a conductive layersurrounding both side surfaces and a front end surface of the dielectricportion which are exposed. Therefore, it is possible to accuratelydetect cancer by the use of the ultra high-frequency signal and to treata diseased portion without damaging tissues around the diseased portion.

Some examples of how an array of sensors can be used for tissuecharacterization are described in WO 2009/010960 assigned to theassignee of the present application.

GENERAL DESCRIPTION

There is a need in the art for a novel EM tissues characterization probehaving multiple sensing elements and the ability of better coupling to atissue being measured.

It should be noted that the term “measurement” actually refers also toexamination, inspection, monitoring of any parameter/condition of thetissue. The term “tissue” should also be interpreted as a general termrelating also to any medium or substance, being for example a tissue ofa subject and being measurable while inside or outside the subject'sbody (in-vivo or ex-vivo measurements).

Operation with higher number of sensing elements increases theresolution of measurements, also enabling the probe to providesufficiently detailed pictorial/spatially resolved representation of themeasured region of the medium (or tissue) under inspection. Known EMtissue characterization probes of the kind specified, namely utilizingmultiple sensing elements are typically limited in a number of suchsensing elements mainly because of technological limits in signalconnection to and from each of the sensing elements. Further, it isoften the case that better coupling between the probe and the tissuerequires certain flexibility of at least a part of the probe. Thisrequirement impose further limitation to the number of sensing elementsthat can be used, in particular to the number of signal connections thatcan be incorporated in a flexible probe.

In general, the invention may be implemented with various types of EMtissue characterization sensors, including for example electric andmagnetic sensors (e.g. RF sensors), temperature, optical and chemicalsensors, etc. In particular, the invention is suitable for use with anytype of sensors that utilize high-frequency EM signals, i.e. requirededicated impedance controlled and, optionally, electromagneticallyshielded signal transmission lines for their operation. The term“impedance controlled” refers to EM signals transferring structures(e.g. signal transmission lines) having well defined, and constant,impedance along substantially the entire extent of the structure.

More specifically, the invention may be implemented for producingpixelated tissue characterization sensor unit that is based on an arrayof near field electromagnetic (EM) sensor cells. The sensor cell is asensing element adapted to measure at least one property of a tissue towhich it is coupled.

The terms near field sensing element or near EM field sensing element(e.g. sensor cell) generally refers to the sensing elements which areconfigured to induce near EM fields (i.e. substantially non radiating EMfields) in the inspected medium/tissue, said EM fields originating froma sensing region defined by the sensing element. Such non-radiating EMfields are typically induced by arranging the sensor conductor elements(e.g. its signal and ground conductors) such that their feature sizeand/or a spacing between them is significantly smaller than onewavelength of the induced EM field. Generally, also the penetrationdepth of a near EM field induced by such sensors is significantlysmaller than one wavelength of the induced EM field, and typically it isof the order of the feature size and/or distance between the conductorelements of the EM sensor. Tissue characterization near field sensorsare typically operated in high frequencies, i.e. from 100 KHz to 5 GHz(for example in the RF, MW regimes).

As indicated above, having a sensor unit including multiple sensor cellsis generally advantageous since it allows to map the properties of atissue with greater resolution and to identify more easily andaccurately transition regions between different tissues for examplebetween healthy and cancerous tissues. An EM tissue characterizationsensor unit (probe) having more than a few sensor cells imposes severalrequirements on the configuration of both the arrangement of sensorcells and the signal feed structure (also referred to as a signaltransmission structure) transmitting the EM signals to and from thesensor cells. This is because, on the one hand, the operation andmeasurement accuracy of many types of tissue characterization sensorcells is dependent on the coupling (e.g. attachment) of the sensor cellsto the tissue. On the other hand, impedance controlled andelectromagnetically shielded signal feed lines are typically cumbersomestructures, and thus providing multiplicity of such feed lines to thesensor cells impairs the flexibility of the sensor unit and the abilityof providing sufficient coupling between each of the sensor cells andthe tissue to be inspected.

According to some aspects of the invention, a sensor unit may include aflexible signal transmission structure including multiplicity ofimpedance controlled and optionally also partially electrically isolated(spatially distanced from each other and/or electrically shielded)signal connection lines suitable for transmitting measurement data inthe form of EM signals to and/or from the multiple sensor cells.

To this end, the flexibility and the configuration of the signaltransmission structure provide several advantages, for example allowingaccommodation of the sensor unit within a flexible lead (guide) such asa lumen where the flexibility of the signal transmission structureenables guiding the lumen within narrow and/or twisted pathways towardsa desired region of inspection. Also, when the sensor unit isaccommodated within a housing or guide, the flexibility of theconnection lines allows back and forward (e.g. elastic) movement of thesensor's “head” with respect to the housing thus also enabling tocontrol the extent by which the sensor's head protrudes from thehousing/guide. The movement enables to control the degree ofattachment/detachment from the inspected medium and allows protection ofthe sensor's head while it is not in use.

Moreover, the flexibility of the connection lines allows to achieveminimal footprint of the sensor unit by enabling to orient substantiallyonly the sensing surface of the sensor unit in the direction of theinspection, i.e. the sensor unit when in operation faces the mediumsubstantially only by its sensing surface. The sensing surface of asensor unit is a surface containing multiple sensing regions of multiplesensor elements or sensor cells, where the sensing regions are arrangedin a spaced-apart relationship. In this connection, it should beunderstood that generally a sensing region is not limited to a planarregion but rather is typically a volumetric region. Hence, sensingsurface is a physical surface of the sensor unit intersected by all thesensing regions. Such reduction of the footprint can be achieved byenabling bending of the flexible signal transmission structure (e.g. in90°) at the vicinity of the boundary between the signal transmissionstructure and the sensor (e.g. the sensor's sensing surface). Thus, thesurface of the sensor unit by which it is coupled to a region ofinterest in the medium is of a size close to the size of the activeregion of the sensing surface occupied by the multiple sensing regions.A region of interest is actually a volume of the medium which is probed,or interrogated, by the sensor unit. This volume is defined by thesensing surface and by the penetration depth of the near field into themedium (which is set by the structure of the near filed of the sensingcell). It should be understood that the region of interest of a subjectis defined per a measurement site.

It should be noted that in some types of tissue characterization sensors(e.g. such as EM sensors configured to induce near EM fields that extendfrom the sensor's sensing surface into proximate regions of a tissuecoupled thereto), good coupling between the sensor sensing surface andthe tissue, without gaps (e.g. air gaps) between them, provides moreaccurate and stable tissue characterization measurements. Hence,according to some embodiments of the invention, sufficient couplingbetween the sensor cells (e.g. and thus coupling the sensor, includingthe sensing surface) and the inspected tissue/medium is obtained byconfiguring the sensor as a flexible structure that allows firmattachment of the sensing surface, and the sensing regions thereon(which are associated with the sensor cells), to the tissue.

It should, however, be understood that some types of sensors such asradioactive field sensors or far EM field (radiating) sensors can beoperated with or without direct contact with the tissue or with lesssensitivity to the degree of attachment with the tissue. In someembodiments of the present invention, the sensor unit is made in theform utilizing flexible circuit techniques such that all the elements ofthe sensor unit (e.g. the sensor's head and the signal transmissionstructure) are flexible while in other embodiments certain parts such asthe sensor's head and or connector elements are rigid and the sensorunit is fabricated by utilizing rigid-flexible circuit techniques. Aflexible sensor head is advantageous foranalyzing/examining/probing/querying/investigating the EM properties(dielectric properties) of a non-planar substance surface, and fordynamic conforming of the sensor surface to an examined substancesurface.

Flexible or Rigid-Flexible circuits (also known as flex-based circuits)are typically manufactured by patterning arrangements of printedconductor configurations (electrical traces) on a base material (i.e.known as the flexible laminate material) with or without flexible coverlayers. In general, flexible circuits are produced in methods which aregenerally parallel to those of printed circuit board constructions.These include, for example, single-sided flexible circuits, double-sidedflexible circuits, multilayer flexible circuits (having three or moreconductor layers), combinations of flex and rigid circuits, andflex-rigid circuits. As flexible laminate material is generally eithersingle sided or double sided metal clad, when multilayer flexiblecircuits are manufactured, the layers of the circuit are bonded bybondply or sheet adhesive and electrical connections between the layersare generally made by plated-through holes interconnections.

The following are some examples of the flexible circuit base materials,also known as flexible metal clad dielectrics or flexible laminatematerials, which might be used in the fabrication of the sensor unit ofthe present invention: Pyralux AP 8535R Adhesiveless double side copperclad polyamide (Kapton) by Dupont company; UPISEL-N BR 1120 Adhesivelessdouble side copper clad polyamide by UBE company; Pyralux AC 181200RAdhesiveless single side copper clad polyamide by Dupont company;UPISEL-N SR 1220 Adhesiveless single side copper clad polyamide by UBEcompany; Pyralux LF 7011R Adhesive bonded double side copper cladpolyamide by Dupont company; Pyralux LF 7041R Adhesive bonded singleside copper clad polyamide by Dupont company; Pyralux LF 0230 polyamidecoverlay by Dupont company; Pyralux FR 0131 polyamide bondply by Dupontcompany; Pyralux LF 0300 sheet adhesive by Dupont company. It should benoted that other suitable materials can be used in the invention aswell.

The requirement for flexibility of the signal transmission structuregenerally leads to, or results in, the construction of this structure,incorporating the minimal number of conductive layers and a minimalspacing between these conductive layers. This type of constructionimposes restrictions on the configuration of signal lines within thesensor, the sensor being integral with the signal transmissionstructure.

Since the high frequency signals are susceptible to EM interferences, itis preferable to electrically isolate signal lines associated withdifferent sensor cells from each other to prevent a cross talk betweenthe different cells. Although this may generally be achieved by passingthe signal line(s) towards and away from a specific sensor cell along apath outside of other cells, such a solution would require certainminimal separation between the sensor cells to accommodate a path forthe signal lines, thus reducing the fill factor of sensing regions(formed by a plurality of the sensor cells) within a sensing surface ofthe probe. Also, increase in the number of sensor cells (e.g. per unitarea in order to provide higher spatial resolution or in order toenlarge the sensing area), generally requires passing a greater numberof signal lines. This is generally achieved by either further increasingthe separation/spacing between the sensor cells within a sensing surfaceand reducing the fill factor of the sensor unit, or by increasing thenumber of signal lines per unit area (signal line density) thusaffecting the interference and cross talk between the lines.

However, in accordance with some embodiments of the present invention, asensor unit having high number of sensor cells (e.g. arranged with highspatial resolution) is implemented without impairing or restrictingeither one of the fill factor of the sensor or its signal to noise ratio(SNR). This is achieved, as is further exemplified below, by allowingthe signal lines associated with sensor cells to traverse “beneath” andacross the sensing regions of other sensor cells while beingelectromagnetically shielded from said sensing regions. In other words,the signal line can be arranged such that its projection onto thesensing surface intersects the sensing region. This allows to maintainboth the sufficient spacing between the signal lines (e.g. providinggood electromagnetically isolation) and the minimal spacing between thesensing regions of the sensor cells, allowing high fill factor. Hence,preferably, the multiple signal lines associated with the sensor cellsare configured to increase SNR of the sensor unit by reducing/minimizinginterferences caused for example by a cross talk between the signallines.

A tissue characterization probe of the present invention includes asensor unit includes multiple spaced-apart sensing regions located in asensing surface and associated respectively with an array of multiplesensor cells. The sensing surface may contain a relatively large numberof sensing regions for example more than 5 sensing regions andpreferably more than 35 sensing regions. Additionally or alternatively,the sensing surface may be characterized by a desirably high resolution,for example more than 5 sensing regions per 35 mm² area and preferablymore than 35 sensing regions per 35 mm² area. The sensing surface may becharacterized by high fill factor of the sensing regions arranged in aspaced-apart relationship such that the area of the spaces between thesensing regions does not exceeds 50% from the area of the sensingregions, preferably not exceeding the 10% of said area. The size of thesensing surface ranges from about 1 mm to 10 cm. The size of the sensingregion of the sensor cell (the projection of the sensing region onto thesensing surface) ranges from about 0.5 mm to about 5 mm. This parameterdefines the upper limit of a range of the minimal feature sizedetectable by the sensor unit.

According to one broad aspect of the invention, there is provided asensor unit for use in measurements on a subject. The sensor unitcomprises a near field electromagnetic sensor, and a flexible signaltransmission structure. The sensor comprises a sensing surface by whichthe device faces a region of interest of the subject, and an array ofsensor cells each configured to define a sensing region surrounded by anelectrically conductive material, an array of the sensing regions beingarranged in a spaced-apart relationship within said sensing surface. Theflexible signal transmission structure is integral with the near fieldelectromagnetic sensor such that the signal transmission structure andthe near field electromagnetic sensor have at least one commoncontinuous surface. The flexible signal transmission structurecomprises: a first layer including an array of signal connection linesassociated with the sensor cells (e.g. being electricallyconnected/coupled, directly or not, to respective elements of the sensorcells), and a second electrically conductive layer electrically coupledto said electrically conductive material of the sensor.

The signal transmission structure and the near field EM sensor may beconfigured for providing impedance controlled signal transmission alongto and from the sensing regions.

Preferably, each of at least some of the sensor cells comprises an innerconductor element coupled to the inside of the respective sensing regionand electrically coupled to the respective one of the signal connectionlines. Thus, the signal connection lines are associated with the sensorcells by electrical connection/coupling of the signal transmission linesto the inner conductor elements of the sensor cells. At least some ofthe sensor cells may be configured as a resistive type sensor(comprising the inner conductor element electrically insulated from thesurrounding electrically conductive material, with or without anelectrical insulator material covering the sensing region) or inductivetype sensors (the sensing cells being connected to the electricallyconductive material surrounding the respective sensing region).

Preferably, the flexible signal transmitting structure has at least oneflexible band configured for bending with respect to the sensor with aradius of curvature smaller than a characteristic dimension of saidsensor. Such bending and flexibility of the band(s) allow for reducingthe footprint of the sensor unit (i.e. the size of its surface by whichit is coupled to the tissue) and also for enabling repetitive movementof the sensor unit with respect to its housing.

In some embodiments of the invention, the sensor is configured as amulti-layer structure, e.g. comprises first and second sensor layers.The first sensor layer comprises a plurality of signal lines, which areelectrically coupled to the signal connection lines of the signaltransmission structure (the signal connection lines are thus associatedwith the corresponding sensor cells). The second sensor layer comprisessaid electrically conductive material and defines the sensing surface ofthe sensor unit. The second sensor layer is electrically coupled to thesecond electrically conductive layer of the signal transmissionstructure. Considering the sensor cells' configuration with the innerconductor elements, the signal connection lines of the signaltransmission structure are electrically coupled to the inner conductorelements of the sensor cells via the signal connection lines of thesensor.

In some embodiments, the signal lines (at least some of them) areassociated with the respective sensing regions and extend in the firstsensor layer along respective paths, such that a projection of each ofthese paths onto the sensing surface is located outside all othersensing regions. In some other embodiments, the signal lines extend inthe first sensor layer along respective paths, such that a projection ofeach of these paths onto said sensing surface intersect with one or moreof the other sensing regions.

The sensor unit may be configured with an additional electricallyconductive sensor layer located within the sensor in between the firstand second sensor layers. This additional conductive sensor layer hasspaced-apart signal transmission regions configured as substantiallynon-conductive regions aligned with at least some of the sensingregions. The signal transmission regions are substantially smaller thanthe corresponding sensing regions, thereby providing by said additionalconductive sensor layer an electrical screening of at least a portion ofthe signal lines from the sensing regions.

The additional conductive sensor layer may be configured to provideelectrical screening of the signal lines extending along paths theprojections of which onto said sensing surface intersect one or more ofthe sensing regions.

In some embodiments, at least some of the signal lines of the firstsensor layer terminate within at least some of the sensing regionsassociated therewith. The signal lines are connected, at theirtermination within the sensing regions, with the inner conductor elementprotruding from the first sensor layer towards the sensing surface, suchthat the electrically conductor elements induce electromagnetic fieldprofile extending outwards from the sensing surface through said sensingregions.

As indicated above, the signal transmission structure preferablycomprises one or more flexible bands capable of bending with respect tothe sensor. Such one or more bands may extend from the sensor along oneor more directions.

In some embodiments, at least one of the sensor cells is configured andoperable as a reference cell. Such reference cell is configured to besubstantially insensitive to effects of a region of interest of thesubject to which the sensor is coupled during operation.

Preferably, the signal transmission structure is configured as aflexible planar microstrip having a plurality of layers including thefirst and second layers being flexible planar layers. Alternatively, oradditionally, the signal transmission structure may be configured as aflexible planar strip comprising a plurality of layers including thefirst and second layers, and additional electrically conductive layer,where the first layer is enclosed between the second and the additionallayers.

According to another broad aspect of the invention, there is provided asensor unit for use in measurements on a subject, the sensor unitcomprising: a near field electromagnetic sensor comprising a sensingsurface by which the device faces a region of interest of the subject,an array of sensor cells each configured to define a sensing regionsurrounded by an electrically conductive material, an array of thesensing regions being arranged in a spaced-apart relationship withinsaid sensing surface; and a flexible signal transmission structureintegral with said near field electromagnetic sensor such that thesignal transmission structure and the near field electromagnetic sensorhave at least one common continuous surface, said flexible signaltransmitting structure having at least one flexible band configured forbending with respect to the sensor with a radius of curvature smallerthan a characteristic dimension of said sensor.

According to yet another broad aspect of the invention, there isprovided a sensor unit for use in measurements on a subject, the sensorunit comprising:

a near field electromagnetic sensor comprising an array of sensor cellseach comprising a sensing region and an inner conductor element locatedwithin said sensing region, the sensing regions of the sensor cellsbeing arranged in a spaced-apart relationship within a sensing surface;and

a flexible signal transmission structure integral with said near fieldelectromagnetic sensor, said flexible signal transmission structurecomprising a first layer including signal connection lines electricallycoupled to the inner conductor elements respectively.

According to yet further aspect of the invention, there is provided asensor unit for use in measurements on a subject, the sensor unitcomprising:

a near field electromagnetic sensor comprising a sensing surface bywhich the device faces a region of interest of the subject, an array ofsensor cells each defining a sensing region surrounded by anelectrically conductive material and comprising an inner conductorelement coupled to the inside of the sensing region, an array of thesensing regions being arranged in a spaced-apart relationship withinsaid sensing surface; and

a flexible microstrip which is integral with said near fieldelectromagnetic sensor and is capable of bending with respect to thesensor, said flexible microstrip comprising a first conductive layerbeing an extension of said electrically conductive material and a secondconductive layer carrying an array of signal connection lineselectrically coupled to said inner conductor elements.

In yet another broad aspect of the invention, there is provided a sensorunit for use in measurements on a subject, the sensor unit comprising:

a near field electromagnetic sensor comprising an array of sensor cellseach comprising a sensing region and an inner conductor element locatedwithin said sensing region, the sensing regions of the sensor cellsbeing arranged in a spaced-apart relationship within a sensing surface;and

a flexible signal transmission structure integral with said near fieldelectromagnetic sensor, said flexible signal transmission structurecomprising a first layer including signal connection lines electricallycoupled to the inner conductor elements respectively.

The invention also provides a sensing device comprising one or more ofthe above-described sensor units.

Also, the invention provides a novel measurement device for use inmeasurements on a subject, where the measurement device comprises: theabove-mentioned sensing device, and a calibration and probe control unit(CPC) which is integral with said sensing device and which is configuredfor connecting to a network analyzer. The CPC preferably comprises anumber of terminals associated with a plurality of calibration loads ofknown RF reflection coefficients respectively and comprises a memoryutility carrying recorded data indicative of the RF reflectioncoefficients and recorded data indicative of RF transfer coefficients ofthe CPC unit, thereby enabling calculation of the RF response of each ofthe sensor cells within the sensing surface of the sensor unit, whileremaining the sensor unit integral with CPC unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, embodiments of the invention will now be described, byway of non-limiting examples only, with reference to the accompanyingdrawings, in which:

FIGS. 1A and 1B show a schematic illustration of an example of a sensorunit, shown respectively before and after assembling the sensor unit ona fixture;

FIG. 2 is a schematic illustration of a sensing device according toanother example of the invention, where the sensing device is formed bytwo sensor units generally similar to that of FIGS. 1A-1B;

FIGS. 3A to 3J show examples of the configuration of a sensor cell andarrangement of cells suitable for use in the sensor unit of the presentinvention, where FIGS. 3A, 3C, 3E, 3F 3H and 3J exemplify sensor cellshaving a hexagonal geometry of the sensing region contour, FIGS. 3B, 3Gand 3I exemplify sensor cells having a rectangular geometry of thesensing regions, and FIG. 3D exemplifies sensor cells having atriangular geometry of the sensing regions; FIGS. 3A, 3E and 3Fexemplify sensor cells having inner conductor elements of a circularcross-section at the distal end, and FIGS. 3G-3J show sensor cellshaving various other geometries of the cross-section at the distal endof the inner conductor elements; FIGS. 3A, 3E-3G show sensor cells inwhich the inner conductor element is electrically insulated from thecontour of the respective sensing region and FIGS. 3H-3J show sensorcells having their inner conductor element electrically connected to thecontours of the respective sensing regions;

FIGS. 4A to 4C show different cross-sectional views of a sensor unitaccording to an example of the invention;

FIG. 4D exemplifies more specifically a reference sensor cell suitableto be used in the sensor unit of the invention per the embodiment ofFIGS. 4A-4C;

FIGS. 4E and 4F exemplify by a schematic illustration the sensor unitshaving respectively single-band and four-band configuration of thesignal transmission structure;

FIGS. 5A and 5B show examples of the impedance controlled signaltransmission structure suitable to be used in the sensor unit of thepresent invention FIG. 5A shows a strip planar structure, and FIG. 5Bshows a micro strip planar structure;

FIGS. 6A and 6B show two examples of the configuration of signaltransmission bands suitable to be used in a signal transmissionstructure of the sensor unit according to the invention, where theexample of FIG. 6B has an additional conduction layer as compared to theexample of FIG. 6A;

FIG. 7A shows graphically a typical stress-strain diagram of a multilayer flexible circuit structure.

FIGS. 7B and 7C illustrate the flexibility characteristics of twoexamples of flexible circuit structures, having different arrangementsof layers;

FIGS. 8A to 8C show different cross-sectional views of a sensor unitaccording to yet another example of the invention;

FIG. 8D exemplifies more specifically a reference sensor cell suitableto be used in the sensor unit of the invention per the embodiment ofFIGS. 8A-8C;

FIG. 9A-9D exemplify a relation between the signal lines and sensingregions in the sensor unit according to the invention, where FIG. 9Ashows a signal layer of the sensor, FIGS. 9B and 9C show two examples ofdifferent configurations of the conduction layer providing respectivelyhigh fill factor of the sensing regions, and high SNR with reducedcrosstalk; and FIG. 9D shows an enlarged view of a portion of theconfiguration of FIG. 9B;

FIG. 10A shows a side cross-sectional view of a sensor unit according toanother embodiment of the present invention, configured to enable highsignal to noise ratio and high spatial resolution and/or high fillfactor;

FIGS. 10B and 10C more specifically illustrate two different examples ofthe layers' structure in the sensor part of the sensor unit;

FIG. 11 is a block diagram of a measurement system comprising ameasurement device utilizing sensor unit(s) of the present inventionintegral with a calibration and probe control (CPC) unit; and

FIGS. 12A and 12B more specifically exemplify the configuration of themeasurement device of FIG. 11.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Reference is made to FIGS. 1A and 1B illustrating schematically a sensorunit 100 according to an embodiment of the present invention. In thesefigures, the sensor unit 100 is shown respectively before and afterassembling the unit on a fixture 150. Sensor unit 100 includes anintegral structure including a sensor or sensor head 110 and a flexiblesignal transmission structure 120. The configuration is such that thesensor and the signal transmission structure have at least one commoncontinuous surface. Also, both the sensor and the signal transmissionstructure are substantially flat. As also exemplified in the figures, anappropriate signal connector structure 160 is provided for electricallyconnecting signal transmission structure 120 to a control unit/signalgenerator/signal analyzer (not shown here).

In this example, sensor unit 100 is configured for tissuecharacterization, by providing data indicative of the type of theinspected tissues and/or indicative of boundaries and transitionsbetween different tissue types along the sensing surface 108. Sensor 110includes a plurality 111 of sensor cells 112 arranged in a spaced-apartrelationship within a sensing surface 108. The sensor cells areappropriately distributed within/spanned across the sensing surface,e.g. tiling or covering the sensing surface 108. Each sensor cell isoperable to inspect/measure/characterize/examine/probe/query/investigateat least one characteristic/parameter of a tissue to which the sensingregion is coupled (either by direct contact or by proximity to thetissue).

It should be noted that the sensor unit can be associated with anappropriate calibration system, including a calibration unit connectableto a network analyzer. This is schematically illustrated in FIG. 11,showing, by way of a block diagram, a measurement system, generallydesignated 10. The system 10 includes a measurement device 12connectable to an analyzer 16. The measurement device 12 of the presentinvention includes one or more sensor units 100 and a calibration andprobe control (CPC) unit 12B. The analyzer 16 includes a networkanalyzer 14, and also a suitable communication unit (not shown) forhandling digital and/or analog communication with the CPC unit 12B.

The network analyzer 14 may be of any known suitable type and thereforeneed not be described in details, except to note that it is configuredand operable for transmitting and receiving RF signals. Network analyzer14 may be configured and operable as a vector network analyzer (VNA),for recording both the relative amplitude and the phase of RF signals.Network analyzer 14 is configured for carrying out the following:transmitting and receiving RF signals via its signal ports; analyzingthe received signals to determine the amplitude and, optionally, phasethereof which are indicative of the signal interaction with calibrationloads; and delivering the calibration correction parameters. Networkanalyzer 14 is also configured for measuring an RF response of themeasurement device 12 using the calibration correction parameters. Theanalyzer 16 may have additional features, for example may be responsiblefor security issues to prevent reuse of the measurement device 12 orinstallation of other non-authorized measurement device in the system.Analyzer 16 may also provide at least one of the following facilities tomeasurement device 12: electrical power supply, means for handlingdigital and/or analog communication with measurement device 12,vacuum/pressure communication 19, a liquid dispensing line, opticalsignal communication, ultrasound signal communication, as well asprovide control and power to an ablative/cutting apparatus/tool inmeasurement device 12, user and/or machine input and/or output, andcontrol of other types of probes to be used in measurement device 12.

FIGS. 12A and 12B show specific but not limiting examples of theconfiguration of the measurement system 10. The measurement device 12includes a sensor unit 100 and a CPC 12B integral with the sensor unit100, which are accommodated in a common housing 12C. The sensor unit 100is connected to the CPC 12B via a cable with an appropriate connector.In the example of FIG. 2A, there is only one RF signal connection (RFport connection) between the analyzer 16 and the measurement device 12.In the example of FIG. 2B, there are two RF signal connections (RF portconnections) between the analyzer 16 and the measurement device 12. Asshown in the figure, a vacuum/pressure communication line may be usedfor providing vacuum/pressure communication 19 to the sensor unit 100.

It should be appreciated that embodiments of the present invention mayutilize more than two RF signal connections between analyzer 16 andmeasurement device 12. There may generally be n such RF signalconnections (RF port connections) between the analyzer unit andmeasurement device, n being an integer equal to or greater than 1.

The CPC unit 12B is connected to the sensor unit 100 via an RF gradeconnector C₅ (for example SMA). Turning back to FIGS. 1A and 1B, thesignal connector structure 160 may be configured as the RF gradeconnector to provide an interface that can define a calibration plainand give repeatable measurement results.

The CPC unit 12B includes a number of terminals associated with aplurality of calibration loads of known RF reflection coefficientsrespectively and includes a memory utility. The latter carries recordeddata indicative of the RF reflection coefficients and recorded dataindicative of RF transfer coefficients of the CPC unit. Thisconfiguration enables calculation of the RF response of each of thesensor cells within the sensing surface of the sensor unit, whileremaining the sensor unit integral with CPC unit. It should beunderstood that the CPC may also be used for selectively directing EMsignals to one or more sensor cells.

Preferably, the CPC unit 12B (implemented as a printed circuit board) isenclosed within a housing, having an RF cover, to provide mechanicalstrength and electromagnetic immunity to the CPC unit 12B. Mechanicalstrength of the housing enables better calibration by eliminatinggeometrical distortion, which may occur, for example, due to mechanicalstresses or environmental changes of the CPC unit. This distortion mayresult in changes in the propagation of RF signals within the CPC unit,leading to degradation in calibration performance. Electromagneticimmunity of the housing enables better calibration by reducing RFinterference of the CPC unit 12B with the sensor unit 100, and byreducing RF interference of external RF sources with the CPC unit 12B.Connectors of CPC unit 12B may be integrated into the housing. Housingmay be constructed to enable operation of measurement device 12 invarious environmental conditions, and to enable sterilization of themeasurement device, by use of radiation and/or gas.

The calibration unit 12B can generally have any suitable configuration,preferably either one of those disclosed in the co-pending Internationalapplication PCT/IL2009/000611, assigned to the assignee of the presentapplication, and which is incorporated herein by reference.

It should be understood that multiple sensor cells enable to spatiallymap properties of a medium or tissue facing the sensing surface, withspatial coverage and resolution according to the number and size of thesensor cells. Also, the size of the sensor cells determines the featuredetection size of the sensor 110 as each sensor cell integrates over thevalue of the properties of the medium within (e.g. beneath) the sensingregion of the sensor cell. Hence, such spatial mapping may providepictorial view of the spatial distribution of values of different tissueparameters measured by the sensor cells with certain minimal featuresize corresponding to the areas of the cells' sensing regions. Such apictorial view of a medium or tissue facing the sensing surface may alsobe regarded as a pictorial representation, spatial representation,spatial resolved detail/spatial resolved presentation/spatial resolveddescription/spatial resolved depiction. It should be understood that thesensors cells may be of the same type (e.g. measuring/inspecting thesame parameters of the tissue) or of different types. The sensor celltypes may include inter alia radio frequency (RF) and/or micro wave (MW)sensors, as well as one or more of other electric and magnetic sensors.

More particularly in the present example, sensor 110 is configured andoperable as a near-field EM sensor including array 111 of near field EMsensor cells 112 that are configured to induce, within tissue regionslocated proximate to the sensor's sensing surface, near EM fieldscorresponding to signals transmitted to this tissue region from a signalgenerator. The configuration and strength of the induced fields, perspecific sensor structure (specific arrangement/configuration and typesof sensor cells), depend on the dielectric properties of the tissueregions adjacent/in close proximity to the sensor's sensing surface.Some examples of the configuration of the sensor cell and themultiple-cell arrangement will be described further below.

In the example of FIGS. 1A and 1B, the integral sensor unit 100 isfabricated by the so-called flexible or rigid-flexible circuittechniques that allow conduction of multiple signal lines to and fromthe sensor 110 in a substantially flat and elastic arrangement thusproviding flexibility of certain parts/regions of the sensor unit. Inparticular, flexibility of regions 102 of the signal transmissionstructure 120 near its boundary with the sensor 110 (sensor head) allowsto wrap the signal transmission structure 120 (e.g. about the fixture150) with a tight (small) bending radius. This allows for reducing afootprint of the sensor unit. Also, flexibility of some other regions ofsensor unit 100, such as regions 104 of signal transmission structure120, provides for repetitive, repeatable, elastic movement of thesensor's head 110 with respect to its connectors 160, thus allowingrelative movement of the sensor with respect to a housing or guide (notshown) in which the sensor might be accommodated. It should be notedthat the technique of the present invention while utilizing theflexibility of the transmission structure of the sensor still enablespassage therethrough of a plurality of high frequency signaltransmission lines to the sensor 110.

Referring now to FIG. 2 there is illustrated schematically a sensingdevice utilizing the principles of the invention. Here, the device isformed by two sensor units 100 and 100′ configured generally similar tothe sensor illustrated in FIGS. 1A and 1B but being of differentgeometries. In order to facilitate understanding of the invention, thesame reference numerals are used to designate elements common in all theexamples of the invention. The two sensor units 100 and 100′ aresimilar, each including a sensor (110, 110′) and a flexible signaltransmission structure (120, 120′), and are geometrically complementarydefining together a two-part sensing head 110-110′ having arrays ofsensing cells. The sensor units are fabricated as planar flexibleintegrated structures (e.g. utilizing the flexible circuit techniques)which are then folded each forming a semi-cylindrical shape of itssensor, the two sensors defining the cylindrical sensing head. Thesensor cells are arranged within a circumference of the cylindricalsensing surface formed by surfaces 108 and 108′ of sensors 110 and 110′respectively. This geometry is especially suited to applicationsrequiring a tubular sensor unit (e.g. insertable into a lumen) andcapable of lateral sensory. Here also, flexibility of regions 104 ofsignal transmission structure 120 provides for elastic movement of thesensor's head with respect to the lumen.

It should be understood that other configurations and geometries ofsensor unit 100 may be employed. These include, but are not limited to,sensors configured for measuring on excision surface, cut surface,excised tissue, branched lumens, body organ contours, and skin. Also,sensor unit 100 may be provided with, but not limited to, fixed probes,hand held probes, endoscopes probes, laparoscopic probes, and roboticprobes.

Reference is made to FIG. 3A showing the configuration of a near fieldEM sensor cell according to a specific but not limiting example. Thefigure shows a cross sectional view of the sensor cell 112. Cell 112 isconfigured as a Near field EM sensor cell 112 and defines a sensingregion 114 functioning as an aperture/opening or window with respect tothe EM fields (region in which the EM fields induced by the sensor cellreside/exist), an inner conductor element 118 having opposite, distaland proximal ends (with respect to the inside of the sensor unit)accommodated such that the distal end is located within sensing region114, and an electric conductive material 116 surrounding sensing region114 e.g. forming an electrically conductive contour/boundary at theperimeter of the sensor cell. It should be understood that generally asensing region 114 is not limited to a planar region but rather istypically a volumetric region. The distal end of inner conductor element118 is located within the sensing region, while not necessarily in thesensing surface, e.g. being below the sensing surface. The distalportion of the inner conductor element is surrounded by the electricallyconductive contour. It should be understood that inner conductor 118 isseparated from electrically conductive contour by dielectric material(s)of the sensor 110 within sensing region 114. As will be describedfurther below, inner conductor element 118 by its opposite (proximal)end portion is electrically coupled to (e.g. physically connected with)a signal line (not shown here).

The inner conductor element 118 may be, for example, in the form of anelectro-plated through-hole traversing across some layers of amulti-layer “flexible circuit” sensor. When sensor cell 112 is operated(i.e. when EM signals are transmitted to the sensor), it functions as anear field EM sensor inducing the near field EM fields within itssensing region 114, and thus in a tissue region located in the vicinityof sensing region 114. The type, extent and magnitude of the EM fieldsinduced in said tissue region is dependent on the electricalcharacteristics of the tissue and on the frequency of the inducingsignals. Hence, the analysis of the type, and magnitude of the EMsignals induced in said tissue region provide data indicative of thecharacteristics of the tissue in the vicinity of the sensing region.

The cell contour may be of any suitable shape, e.g. hexagonal as shownin FIG. 3A and also in FIGS. 3C, 3E, 3F, 3H and 3J, as well asrectangular as shown in FIGS. 3B, 3G and 3I and triangular as shown inFIG. 3D. As further exemplified in the figures (see for example FIG.3B-3D), the cells may be arranged such that the sensing regions formvarious two dimensional arrays (tiling). The cells may also be arrangedas one dimensional array (not shown). Inner conductor element 118 mayalso be of any suitable cross sectional shape, e.g. circular (FIGS. 3A,3E and 3F) or other shapes (FIGS. 3G to 3J).

In some embodiments of the invention, the sensor cells (or at least someof them) are configured as a resistive type EM near field sensor. Eachof such resistive type sensors includes the inner conductor element 118electrically insulated from the surrounding electrically conductivematerial (contour) 116. This is shown in the examples of FIGS. 3A,3E-3G. The resistive type sensor cell may also include an electricalinsulator material covering the sensing region so as to insulate therespective sensor cell from the subject, as will be described furtherbelow. Alternatively, the resistive type sensor cell may be configuredto perform measurements while both the inner conductor element 118 andthe surrounding electrically conductive material 116 are in directcontact with the subject, as will be described below with reference toFIGS. 4A-4C.

According to some other embodiments shown in FIGS. 3H-3J at least someof the sensor cells are configured as inductive type sensors havingtheir inner conductor element 118 connected to the electricallyconductive material 116 surrounding the respective sensing region.

Reference is made to FIGS. 4A-4D illustrating more specificallydifferent cross-action views of a sensor unit 100 according to anembodiment of the present invention. The cross section illustrated inFIG. 4C generally corresponds to a cut taken along a line 191 in FIG.4A.

As shown, sensor unit includes sensor 110, defining a sensing surface108, and signal transmission structure 120. Sensor 110 is configured asa near field EM sensor having a sensing surface 108 by which the sensorunit faces a region of interest of the subject, and an array of sensorcells 112 arranged in a spaced-apart relationship within the sensingsurface. Each sensor cells 112 is configured to define a sensing region114 surrounded by an electrically conductive material 116. The signaltransmission structure 120 is flexible and is integral with sensor 110such that they have at least one common continuous surface (layer) 127.Signal transmission structure 120 has a first layer 125 in which anarray of signal connection lines 122 are located being associated withsensor cells 112 (e.g. being electrically connected/coupled torespective elements of the sensor cells, e.g., the inner conductorelements in the sensor cell configuration of the present example), and asecond electrically conductive layer 126 electrically coupled toelectrically conductive material 116 of the sensor. In the examplepresented in FIGS. 4A-4D, sensor 110 and signal transmission structure120 have two common continuous surfaces: layer 127 and layer 126/117.

Signal transmission structure 120 defines one or more bands electricallyconnected to and integral with the sensor 110. In the present example,the signal transmission structure is a single-band structure 120. Thesignal transmission structure is configured to provide multiple signalconnection lines 122 all located in a common layer 125 and associatedwith the plurality of sensor cells.

The sensor 110 includes an arrangement of signal lines electricallycoupled to the signal connection lines of the signal transmissionstructure 120. An arrangement of such signal lines 128, feeding EMsignals to array 111 of sensor cells 112, is illustrated in FIG. 4B.Also, the electrically conductive material 116 (e.g. the cells'perimeter) forms an electrically conductive layer 117 of the sensor 110(seen in FIG. 4A) which may or may not be grounded when the sensor unitis in operation. The sensor 110 is a multi-layer structure including atleast a first sensor layer 119 (including said signal lines 128) and asecond conductive layer 117. Layers 119 and 117 are electricallyisolated from each other (e.g. by using an electrically isolatinglaminate, adhesive, coating, or an additional isolation layer). In thepresent example, the electrical isolation is obtained by provision of aninsulating (dielectric) layer 127 which serves as a substrate layer forboth the layer 117 and the layer 119 of the sensor 110 and which iscommon also for the signal transmission structure 120.

In some embodiments of the present invention, at least one sensor cellserves as a reference cell, which electromagnetic signal issubstantially not affected from the type of tissue coupled therewith,that is, when the sensor is coupled with the region of interest of thesubject. For example, as shown in FIG. 4D, one of the sensor cells is areference (e.g. dummy) cell 112′, electromagnetically isolated from themedium/tissue. Such isolation can be achieved for example by acontinuous conductive material coverage connecting the inner conductorelement of cell 112′ with its electrically conductive perimeter, oralternatively, as exemplified in FIG. 4D, by disconnecting the signaltransmission line in layer 119 from the measured tissue/medium(eliminating the inner conductor element) and thus providing the desiredelectrical isolation between them. Such a reference cell (e.g. 112′),which is screened from an effect of the tissue portion, may serve forcalibration purposes, e.g. needed because of changes in the propagationof EM signals within the flexible signal transmission structure 120resulting from changes in the shape of signal transmission structure 120during its movement.

It should be understood that the invention is not limited to anyspecific number of bands in the signal transmission structure.Generally, there is at least one such band. As shown in FIG. 4E, as wellas in the above-described examples of FIGS. 4A and 4B, the signaltransmission structure 120 defines the single band. In the example ofFIG. 4F, signal transmission structures 120 suitable to be used in thesensor unit has a four-band configuration. The number of such bands mayvary in accordance with a specific application of the sensor unit, aswell as certain factors such as the number of signal connection linesrequired, the minimal signal to noise ratio required and the dimensionsof the sensor. This is in order to provide sufficient number of signalconnection lines (e.g. in accordance with the number of sensor cells)while preserving a required spacing between the lines to maintaincertain desired electrical isolation thereof and also preserving adesired flexibility (minimal bend radius) at the boundary regions 102between the sensor unit and of the signal transmission structure. Thiscan be achieved by utilizing multiple signal transmission bands, thusimposing minimal restrictions on the length of the sensor's perimeter130 and therefore also on the footprint to the sensor.

As noted above, fitting the array 111 of multiple sensor cells 112 tothe tip of a probe (not shown) enables spatial mapping of certaincharacteristics of the tissue when the sensor cells are similar, and onthe other hand, when different types of sensor cells are used it enablesto measure different properties in proximate regions of the tissue. Itshould be noted, however, that one of the prerequisites for a sensorcomprising a multitude of sensor cells is to provide a number of signalconnection lines 122 (i.e. in the signal transmission structure 120)electrically coupled to the sensor cells and adapted to enable readoutof data (e.g. in the form of an EM signal) therefrom. Providing signaltransmission structure 120 that has multitude of such signal connectionlines may be especially cumbersome when the signal connection lines arerequired to propagate EM signals at high frequencies, for example above1 Mhz. At such high frequencies, EM signals propagate as guided modes(or waves) along the signal connection lines (which function, togetherwith second electrically conductive layer 126, as wave guides) andaccordingly such signals may suffer from various disturbances alongtheir path impairing their accuracy. These disturbances may include, forexample, absorbance and reflectance due to various factors of the signallines such as a change of impedance (e.g. as a consequence of changes inmaterial and/or geometrical dimensions along their propagation path) orinterference and/or crosstalk with other signals (e.g. crosstalk betweendifferent signal transmission lines) due to, for example, lack ofelectrical screening of signal connection lines 122, or due to proximityof signal connection lines 122 to each other.

Accordingly, in order to maintain reliable and accurate signaltransmission, signal transmission structure 120 carrying the EM signalsto array 111 of sensor cells is impedance controlled and optionally alsoelectrically shielded. Generally, such signal transmission structuresinclude at least one signal line which is located with a well defined,fixed, spatial relation to at least one electrically conductive surfaceassociated therewith and arranged in its vicinity. The signal line andelectrically conductive surface are interspaced by a dielectric,non-conductive, material spacer. The spatial relation between the signalline and the conductive surface, as well as the dimensions of the signalline and the material of the dielectric spacer, determine the impedanceof the line. Some examples of such impedance controlled structures areillustrated in FIGS. 5A-5B, in which a strip planar feed structure forsignal transmission, or signal communication, 300A and a micro strip300B planar feed structure are illustrated respectively. Thesestructures comprise similar functional elements including a signalconnection line 310 and one or more conductor surfaces 320 with a fixedspatial relation to the signal line. The signal line and theelectrically conductive surface are interspaced by a dielectric,non-conductive, material spacer (not shown). Conductor surfaces 320 mayalso provide electrical-screening (shielding) to the EM signalspropagating on signal line 310. Generally the strip structure 300Aprovides better electrical-shielding of the signal connection line 310since it includes two conductor surfaces 320 located from both sides ofthe line 310. However, for the same reason, the strip structure isgenerally less flexible than the micro-strip structure 300B (the minimalbend radius below which the structure breaks (or yields, or reachesfatigue), and the minimal band radius for which the structure can beelastically, or reversibly, deformed, are higher in the strip structure300A).

According to the present invention, each one sensor cell 112 (or eachbunch thereof) may be associated with a dedicated signal line (one ofthe lines 128) which is connected with a respective signal connectionline (one of the lines 122) of the signal transmission structure 120.Lines 128 and 122 are configured for propagating EM signals therethroughand thus to and from the corresponding sensor cell(s) 112. This requiresthe signal transmission structure 120 to be capable of transmittingmultiple EM signals (e.g. concurrently) to the sensor cells 112 andpreventing spatial and/or temporal interference between these signals.At the same time, in order to provide a desirably small footprint of thesensor 110 (or sensor head), a tight bending of the signal transmissionstructure 120 is required at the boundary 102 between that structure 120and the sensor 110. A bending radius should preferably be smaller(preferably, much smaller) than the dimension of the sensing surface108, to thereby allow a small footprint of the sensor, i.e. such thatthe sensing surface is substantially equal to a contact area between thesensor unit and the tissue during measurements.

Alternatively (as for example in the embodiment of FIG. 2), oradditionally, the flexibility of the signal transmission structure isrequired in order to provide a relative motion of the sensor relative tothe housing of the sensor unit or relative to the signal connectorstructure (e.g. 160 in FIGS. 1A and 1B). For example, it might bespecifically important when the sensor's housing has a tubular shape(e.g. to be inserted into a lumen) and when back and forward movementsof the sensor unit with respect to the housing is needed.

The above two requirements of the impedance controlled signaltransmission and flexibility are achieved in the present invention byutilizing a planar (i.e. flat) signal transmission structure. It shouldbe understood that the terms “planar” and “flat” used for the purposesof the present application actually signify a relatively thin structureat least within a region thereof where the structure can thus be bent.Also, the sensor unit of the invention has a coplanar configuration inthe meaning that the sensor part and the signal transmission part areintegral with one another presenting a common continuous surface.

Such a planar/flat sensor unit might have a signal transmissionstructure configured as a micro-strip 300B or strip structures 300A asshown in FIGS. 5A and 5B, having a controlled and fixed impedance, e.g.50 ohm or 200 ohm.

It should also be noted that in some cases and for sometypes/configurations of the tissue characterization sensor cells,accurate measurements of the tissue require sufficient and preferablyeven coupling between the multitude of sensor cells 112 and the tissue.In this case it is preferable that also the sensor 110 is flexible andthus it is also configured as a flexible-circuit micro-strip or stripflexible structures. In other cases, however, it is preferable that thesensor 110 is rigid, and in these cases a combination of rigid sensor110 and flexible signal transmission structure 120 can be obtained byutilizing the Rigid-Flexible circuit technology as previously described.

Signal transmission structure 120 in the examples described aboveincludes signal layer 125 in which signal lines 122 are formed beingarranged in a spaced apart relationship (having certain minimal linespacing to minimize/prevent cross-talk), and includes at least oneconduction layer 126 associated with signal layer 125. As noted above,in order to provide high mechanical flexibility of signal transmissionstructure 120, it is preferable to minimize the number of layers in thestructure 120, especially the number of conductive layers that includeelectrically conductive material(s), typically metals, which aretypically less stretchable than insulator-materials layers. Accordingly,in preferred embodiments of the present invention the signaltransmission structure 120 includes a single signal layer 125 and one ortwo conduction layers (only one conduction layer 126 is used in theembodiment of FIGS. 4A-4D) associated with said signal layer 125providing impedance controlled signal transmission and optionallyproviding some electrical screening (shielding) to the signal lines 122.

FIGS. 6A and 6B illustrate schematically two examples of signaltransmission bands 400A and 400B of a signal transmission structureaccording to some other embodiments of the present invention. The signaltransmission band 400A shown in FIG. 6A includes a first signal layer405 that includes two spaced-apart signal lines 411 and 412, and asecond conduction layer 406 that is electrically insulated from thefirst signal layer 405. The signal layer 405 and the second conductionlayer 406 are interspaced by a dielectric, non-conductive, materialspacer (not shown). Signal lines 411 and 412 and conduction layer 406actually form a co-planar arrangement of two micro-strip feed structures401A and 402A, in which a spacing d_(1A) between the signal lines is toprevent cross-talk between signal lines 411 and 412. The spacing d_(2A)between the conduction layer and signal layer, the type of dielectricspacers (not shown), and the width of the signal lines determine theimpedance of the signal transmission structure. It should be understoodthat although in the examples of FIGS. 6A and 6B only two signal lines411 and 412 are shown, typically more than two such signal lines arearranged within each signal transmission band.

Signal transmission band 400B shown in FIG. 6B is generally similar tothe above-described band 400A and distinguishes therefrom in that itincludes an additional conduction layer 407. Signal lines 411 and 412and conduction layers 406 and 407 are arranged, in this example, to forma co-planar arrangement of two strip feed structures 401B and 402B. Alsohere, spacing d_(1B) between the signal lines is to prevent cross-talkbetween signal lines 411 and 412, and spacing d_(2B) is between theconduction layers and signal layer, the type of dielectric spacers (notshown) and the width of the signal lines determine the impedance of thesignal transmission structure. It should also be noted that utilizing astrip configuration as shown in FIG. 6B enables to maintain the samedegree of cross talk between signal lines with a somewhat reducedspacing d_(1B) between them, relative to the spacing d_(1A) required bythe micro-strip of FIG. 6A thus enabling to fit greater number of signallines within a signal transmission band of the same width. On the otherhand, as described above, additional conduction layer 407 and additionaldielectric spacers (not shown) affect and reduce the flexibility ofsignal transmission band 400B. Also, when comparing between amicro-strip and a strip line configuration both having similar impedanceand line width, the strip configuration requires a thicker dielectricsubstrate, thereby also reducing the flexibility of the signaltransmission band 400B.

Thus, the type of signal transmission bands of the signal transmissionstructure is to be designed, inter alia, in accordance with the desiredvalue of such parameters as the degree of allowable cross talk, therequired width of the band and the number of signal lines that are topass therethrough and the required band flexibility (e.g. the minimalpossible bend radius of the transmission band that does not inflictstructural damage to the band). Additionally, in some embodiments theflexibility of the signal transmission structure 120 is required inorder to allow for continuous and repetitive movement of the sensorrelative to the probe housing (e.g. bending of the signal transmissionstructure is operated at the elastic or sometimes in the elastic-plasticregions of the stress-strain curve illustrated below).

Reference is now made to FIGS. 7A-7C exemplifying the principles ofselection of the appropriate layer configurations for the sensor unit inaccordance with a desired flexibility/minimal bending to be obtained.FIG. 7A shows a stress-strain diagram of a typical flexible circuit. Thediagram illustrates a typical Strain ∈ (i.e. the Change in Length l, in%) of the flexible circuit structure as a function of stress σ (i.e.Force/Area) applied to the structure, for example when the structure isbeing bent. As shown in the figure, the response of the structure, i.e.strain ∈, to the applied force, stress σ, can be generally divided intothree regimes: the elastic regime characterized by linear and reversibledeformation of the structure in response to the applied force, in whichthe structure material returns the structure back to its original lengthafter the application of force is released; elastic-plastic regime,which is characterized by a non-linear deformation of the structure(after the force is released, the structure material does not return thestructure completely back to its original form); and plastic regioncharacterized by linear irreversible deformation. It is thus clear thatthose regions of the sensor unit in which repetitive bending of thesensor unit is intended (e.g. regions 104 in FIGS. 1A, 1B and 2) minimalbent radius should be restricted to the elastic and/or elastic-plasticregimes (preferably elastic regime), while in region(s) in which apermanent bent is to be used (e.g. boundary regions 102 in FIGS. 1A and1B) a constant/fixed minimal bent radius within the plastic regime canbe utilized.

It should be noted however that these regimes may vary in accordancewith the layout of the sensor unit structure (i.e. the layersthicknesses and materials). This dependence is exemplified in FIGS. 7Band 7C showing two examples of flexible circuits, having differentlayers structures which include one and two conductive copper layersrespectively. These examples illustrate the dependence of the minimalpossible bent radius on the number, material type and thicknesses of thelayers in the structure within the region to be bent.

FIG. 7B illustrates a flexible circuit structure according to a specificbut not limiting example. The structure includes a single substratelayer S having a thickness D=50 μm, a single copper conductive layer Chaving a thickness of t=35 μm and a cover layer V of a thickness d=50μm. The maximal elongation (linear deformation) E of such structure isgiven by the following formula:

$E = {\frac{\frac{t}{2}}{D + \frac{t}{2} + R} \leq {E_{B}.}}$where E_(B) is 10% in order to avoid breakage, and E_(B) is 0.3% whenconsidering dynamic bending.

Accordingly, the minimal possible Bent Radius is:

$R \geq {{\frac{t}{2} \cdot \frac{1 - E}{E}} - D}$

Hence, for the above parameters, the maximal possible deformation in thedynamic bending regime (elastic) is achieved with the minimal bendradius R≧5.766 mm, while the bend radius for which breakage will notoccur is R≧0.108 mm.

FIG. 7C illustrates a flexible circuit structure according to a specificbut not limiting example. The structure includes a single substratelayer S having a thickness D=50 μm and two copper conductive layers Chaving a thickness of t=35 μm and two cover layers V of a thickness d=50μm arranged as shown in the figure in a self explanatory manner.Generally, the additional layers (generally thicker structure and/ormultitude of conductive layers which are less flexible) limit thebending radius and thus the minimal bend radii (for dynamic andnon-dynamic bending) are greater in this example as compared to that ofFIG. 7B.

Here, the maximal elongation (linear deformation) E of such structurebefore breakage is given by the following formula:

${E = {\frac{\frac{D}{2} + t}{R + d + t + \frac{D}{2}} \leq E_{B}}};$where E_(B) is 10% in order to avoid breakage, and E_(B) is 0.3% whenconsidering dynamic bending.

Accordingly, the minimal possible Bending Radius is:

$R \geq {{( {\frac{D}{2} + t} ) \cdot \frac{1 - E}{E}} - d}$

Hence, for the above parameters, the maximal possible deformation in thedynamic bending regime (elastic) is achieved with the minimal bendradius R≧20.056 mm, while the bend radius for which breakage will notoccur is R≧0.495 mm.

It should be noted that when at least one of the thickness d, D, and tis selected to be lower than those presented in the above example, theminimal bending radius can be made smaller than the value obtained inthe above example. For sensing surface size of about 1-100 mm, theminimal obtainable bending radius E_(B) is significantly smaller thanthe sensing surface size. The desirably small footprint of the sensorunit can thus be achieved.

Turning back to FIGS. 1A and 1B, it should be understood that the radiusobtained for breakage/failure condition sets the limit for the curvatureof boundary regions 102, and the radius obtained for elastic regime setsthe limit for regions 104.

Referring back to FIG. 4C, sensor unit 100 is implemented as anintegrated structure including a stack of three layers includingsubstrate insulating layer 127 from both sides of which the first sensorlayer 119 and the conductive layer 117 are respectively arranged. Itshould be understood that the substrate insulating layer 127 serves as asubstrate also for the signal transmission layer 125 of the signaltransmission structure 120 which is integral with first sensor layer 119and as a substrate for the conductive layer 126 of the signaltransmission structure 120 which is integral with conductive sensorlayer 117. Accordingly, the signal connection lines of signaltransmission layer 125 are integral with signal lines 128 of the sensor.More generally, the respective layers of the sensor 110 and the signaltransmission structure 120 are arranged with one or more commoncontinuous surfaces.

It should be noted that in the present example, the substrate layer 127comprises Polyimide material and that copper is used as conductivematerial for the conductive layers 117, 126 and for the signal lines andsignal connection lines of the layers 119 and 125 respectively.

Reference is made to FIGS. 8A-8D illustrating an example of a sensorunit 100 according to another embodiment of the present invention. Inthis example, the sensor unit includes even higher number of sensorcells than in the example of FIGS. 4A-4D thus allowing enhancedmeasurement resolution and allowing for a smaller minimal detectablefeature size. Accordingly, a higher number of signal lines propagatethrough the signal transmission structure 120. To this end, the signaltransmission structure 120 has two signal transmission bands 120A and120B in which multiple signal lines traverse to different sensor cells.The division of the signal transmission structure 120 into severalsignal transmission bands (in this case two such transmission bands) ismade in order to accommodate more signal lines within the signaltransmission structure 120 without decreasing the spacing between thesignal lines (thus without impairing the EM isolation of the lines) andalso without increasing the footprint of the sensor 110.

In the embodiment shown in FIGS. 8A-8D, the sensor unit is generallysimilar to that of FIGS. 4A-4D. However, while in the example of FIGS.4A-4D the sensor cells are configured to operate in direct contact withthe tissue/medium, in this embodiment the sensor cells 112 are designedto operate while being electrically isolated from the inspected medium.Accordingly, an additional dielectric coating (or layer) 132 isprovided, separating and electrically isolating the conductive elements116 and 118 of the cells 112 from the inspected medium. Also in thisexample there is an additional dielectric layer/coating 134 coveringboth the first sensor layer 119 and the signal layer 125 of the signaltransmission structure 120.

Similarly to the embodiment of FIGS. 4A-4D, in the present example atleast one sensor cell may serve as a reference cell being configured asshown in FIG. 8D. As noted above, in this embodiment the active sensorcells operate without direct electrical contact with the measured tissueand accordingly layer 132 is shown to cover the sensor cells (activecells 112 shown in the figure, but it should be understood that layer132 also covers dummy cell 112′ although in this example it is lesssignificant). Also, in this embodiment the insensitivity of thereference cell 112′ to the characteristics of the measured medium isobtained by extending the distal end of 118′ to cover all the sensingarea 114′ and electrically coupling the inner conductor element 118′ ofcell 112′ to with its electrically conductive perimeter 116′.

FIG. 8C also illustrates an example of the use of a rigid-flexiblecircuit technique in the fabrication of a sensor unit in accordance withthe present invention. The layer structure of signal connector structure160 includes a multitude of layers integral with and substantiallysimilar to the layers of the flexible signal transmission structure 120.Rigidity of the signal connector structure 160 is provided by anadditional rigidizer layer 193 which is connected to the layer structure(e.g. by suitable adhesive). It should be noted that similar techniquesmight be used for rigidizing other parts of the sensor unit such as thesensor's head or parts thereof and/or some regions of the signaltransmission structure.

The sensor cells illustrated in the examples of FIGS. 4A-4D and 8A-8Dare configured as near field EM sensors. In order to provide suchsensors with good measurement accuracy, it is preferable that innerconductor element 118 located within sensing regions 114 of the sensorcell and electrically conductive material 116 surrounding the sensingregions 114 will both be located on the same sensing surface 108 (line108 which designates the sensing surface serves only as guide to the eyeand not as a structural element of the sensor) that faces themedium/tissue during measurements. To this end, inner conductor element118 is connected to a respective signal line in the first sensor layer119 and protrudes to the front side of the sensor towards the sensingsurface 108. When the sensor cell is operated, the configuration ofconductor elements comprising the distal end of inner conductor element118 and conductive material 116 in the perimeter of the sensor cell(being in the sensing surface 108) operate together to induce the EMfield in the vicinity of the tissue/medium close to sensing region 114.Typically, the inner conductor element 118, which is electricallyconnected to a respective signal line 128, carries an EM signal (e.g.constant voltage or alternating voltage at some frequencies), and theconductive material is held at ground potential. This affects aninduction of the EM field within the tissue in close proximity to therespective sensing region of the sensor cell 112 which is the regionenclosed by a perimeter of the electric conductive material 116. Thepenetration depth of the EM field within the tissue is typically of theorder of the size of the sensing region 114 or of the order of thefeature size of the distal end of inner conductor 118. The dimension ofthe sensing region or of the feature size of the distal end of innerconductor 118 thus defines/sets the depth to which the EM fieldspenetrate the medium. Selecting appropriate arrangement of the sensorcells in the sensing surface, e.g. their structure, number, size andfill factor, allows inspection a region of interest having a certaingiven size and located at a certain given depth in the tissue.

It should be understood that all the above considerations, when aimed atproviding a flexible signal transmission structure integral with thesensor 110, create design limitations, or constraints, on the spatialarrangement/routing of signal lines within the first sensor layer 119.

It should be understood that, generally, not only the distal end (e.g.tip) of the inner conductor element 118 (e.g. the section of the innerconductor element 118 which is distal from the first sensor layer 119)induces the EM field within the tissue portion located in front of thesensing region 114, but also additional EM fields are induced within thesame tissue portion by sections of the signal lines which pass withinthe respective sensing region 114. It should be understood that in thepresent disclosure, referring to signal lines passing within the sensingregion designates the signal lines passing within the first (sensor'ssignal) layer 119 and which when projected onto the sensing surface 108pass within the sensing region. An example of such section isillustrated in FIGS. 4A and 4B. In this example, section 195 of a signalline is passing, in the sense described above, within a sensingregion/aperture 196 of sensor cell 197. The section 195 is, in thiscase, a part of a signal line which is associated (e.g. connected toinner conductor element of the cell) with the sensor cell 197, howeverit should be understood that in some cases, signal lines which passwithin (or across) the aperture can be associated with other cells aswell.

These additional EM fields, which are induced, as describe above, bysignal lines passing within the sensing region, introduce an amount ofnoise to the measurement. This noise may be caused by a cross talkbetween the sensing region (aperture) 114 and the signal linesassociated with other sensor cells passing within said sensing region114 or by the additional near field EM fields generated in sensingregion 114 by sections of signal line 119 associated with the samesensing region 114. This leads to an addition of noise (lowering theSNR) due to the non identical (from cell to cell) addition of thesefields to the fields induced by distal portions of inner connectors 118(which are identical from cell to cell).

Referring now to FIG. 9A-9D, examples of a relation between the signallines and sensing regions are more specifically shown. FIG. 9A showsfirst (sensor's signal) layer 119 of sensor 110 in a configuration asillustrated in FIGS. 8A-8C, FIGS. 9B and 9C show two examples ofdifferent configurations of conduction layer 117 of this sensorconfiguration having high fill factor (FIG. 9B) and reduced noise andcrosstalk (FIG. 9C).

FIG. 9A shows that layer 119 includes multiple signal lines 128 that areassociated with different sensor cells (signal lines 128 arranged toterminate within the location of their respective sensor cells). Also,signal lines 128 are shown to be integral with signal connection lines122 of the signal transmission structure and arranged to maintain atleast a certain minimal distance between the lines within the regions ofboth the sensor 110 and the signal transmission structure 120.

FIG. 9B illustrates an example of the sensor 110 including a conductionlayer 117 placed on top of first sensor layer 119 of FIG. 9A. Layer 117in this example includes relatively large sensing regions 114 (windows)having relatively small sized (narrow) spacing d_(s) therebetween.Accordingly, sensing regions 114 occupy a substantial area within thesensor's sensing surface 108 thereby providing a high fill factor of thesensing regions within the sensing surface 108. FIG. 9D shows morespecifically sensor cells 112, 112′ and 112″ and their associated signaltransmission lines

Generally, a high fill factor of the sensing regions in the sensingsurface is desirable in order to increase the sensitivity of the sensorcell to the presence of small feature size properties of the mediumunder monitoring. However, configuring the sensor as herein exemplifiedwith a high fill factor of sensing regions in the sensing surface mighteither impair the sensor's accuracy or allow the use of only a smallnumber of sensor cells thus reducing the applicable resolution of thesensor. This is because the narrow spaces d_(s) allow only a limitednumber of signal lines to traverse between the sensing regions whilebeing electrically shielded therefrom. This is also because a certainminimal spacing between the signal lines has to be maintained inaccordance with a desired degree of electric isolation between adjacentsignal lines (e.g. to prevent cross talk), so that the signal linescannot be all made to accommodate only the regions d_(s). Hence, in thecase of high spatial resolution requirement which in turn requires agreater number of signal lines, the signal lines of different sensorcells would unavoidable pass through the sensing regions of other sensorcells. For example, the portions of signal lines 141′ and 141″associated with cells 112′ and 112″ pass through the sensing aperture114 of another sensor cell 112. As described above, these signal linesinduce additional EM fields within the tissue portion to which thesensing region 114 is coupled and thus impair the accuracy of themeasurements and affect crosstalk between the different sensor cells.Also, since the size of the sensing region in this example is relativelylarge, the portion of the signal line that is associated with arespective sensor cell and which pass through the cell's sensing region114 is also quite lengthy, thus also impairing the accuracy of themeasurement of the sensor cell.

Moreover, as noted above, during operation the sensor cell actuallyintegrates the EM response of a tissue region located in front of itsrespective sensing aperture. The EM response of said tissue regionscorresponds to the spatial distribution of the EM fields generatedwithin the sensing aperture of the sensor cells. Different types ofsensor cells (for example such as those illustrated in FIGS. 3E-3J) aredesigned to induce different spatial configurations of EM fields havingfor example circular, rectangular, hexagonal symmetries. The analysis ofthe tissue characteristics is largely dependent on the spatialconfiguration of the induced fields which in turn might be susceptibleto electrical interferences such as those induced by the sections of thesignal lines passing within the sensing region, for example as describedabove, sections 141′, 141″ (see also FIG. 9D). Hence avoiding/reducingsuch effects of electric interferences by electrically screening thesections of the signal lines passing within the aperture and the sectionof the inner conductor element, other than its distal end, from thesensing regions of the sensor cells, provide tissue characterizationmeasurements with improved accuracy.

FIG. 9C illustrates another example of the sensor 110 includingconduction layer 117 placed on top of the first sensor layer 119 of FIG.9A. Here, layer 117 includes relatively small sensing regions 114arranged with relatively large (broad) spacing d_(s) between them, andaccordingly the portions of signal lines that traverse or pass withinthe sensing regions are small and the cross talk between the sensorcells is minimized. In this example the sensing regions 114 occupy arelatively small area of the sensor's sensing surface 108 thus providinglower fill factor of the sensing regions.

The invention allows for providing a high spatial resolution sensor unitthat has relatively high signal to noise ratio (e.g. crosstalk betweenthe different sensor cells is suppressed) and has relatively high fillfactor of sensing regions. In this connection, reference is made to FIG.10A showing a side cross-sectional view of a sensor unit according toanother embodiment of the present invention. The sensor unit isconfigured generally similar to that of FIGS. 4A-4C and 8A-8C. Morespecifically, the sensor unit includes a sensor 110 and a signaltransmission structure 120 integral with the sensor 110, both havingcommon continuous surface 127. Sensor 110 includes an array 111 ofsensor cells (e.g. 112) which define a respective array of sensingregions (e.g. 114) surrounded by electrically conductive material 116.Sensor 110 includes a first sensor layer 119 containing signal lines 128and a second conduction layer 117 in which the sensing regions are made(e.g. in the form of electrically insulating windows or perforations)and which include the electrically conductive material 116 surroundingthe sensing regions. The sensor cell also includes an inner conductorelement 118 protruding from the first sensor layer 119 towards thesensing surface 108. In order to obtain high signal to noise ratio, aswell as high spatial resolution and/or high fill factor, the portions ofthe signal lines that pass within the sensing regions should beelectrically shielded (screened) from the sensing regions 114themselves. In the present example of FIG. 10A, this is achieved byutilizing an additional conductive layer 140 located in between thefirst sensor layer 119 carrying the signal lines and the secondconductive layer 117 in which the sensing regions are made. Theadditional conductive layer 140 acts as an electrical shield, screeningsignal lines that traverse in the first sensor layer 119, passing withinthe sensing regions, from the sensing regions, and thus from the sensingsurface 108.

An example of the configuration of the additional layer 140 is shownmore specifically in FIG. 10B. Layer 140 is a conductive layer thatincludes an array 144 of signal transmission regions 145 (e.g. in theform of perforations in layer 140), which are substantiallynon-conductive regions and are arranged in a spaced apart relationshipin layer 140 being aligned with at least some of the sensing regions. Inother words, the array 144 of signal transmission regions 145corresponds to the array of the sensing regions associated with thesensor cells array 111. It should be noted that transmission regions 145may be concentric with the sensing regions 114 and be generally smallerthan the sensing regions 114 thereby providing by said additionalconductive sensor layer an electrical screening of at least a portion ofthe signal lines from the sensing regions. Here the additional layer isintegral with the conductive layer 126 of the signal transmissionstructure 120 (only small portion of which is shown).

FIG. 10C illustrates schematically the conduction layer 117 including anarray 130 of sensing regions 114. It should be understood that in theassembled sensor configuration the conduction layer 117 is located abovethe additional layer 140 and faces the tissue/medium to becharacterized. Transmission regions 145 provide access to the innerconductor elements of the sensor cells while electromagneticallyscreening other portions of the signal transmission layer, those passingwithin the sensing regions 114.

The arrangement presented in FIGS. 10A-10C leads to that the structureof the induced EM near field in the sensing region 114 of each of thesensor cells 112 will not be affected by sections of signal linespassing within the sensing regions 114. This leads to an increase in theSNR of the measurements, and thus to an increase in the characterizationcapabilities of sensor 110.

It should be noted that also in this example the sensor unit isimplemented as an integrated structure including a stack of layers.However, in contrary to the previous examples presented, here theconductive layer 126 of the signal transmission structure 120 isintegral with the additional sensor layer 140. In this connection itshould be noted that in this example, in order to provide highflexibility of the boundary 102 between the sensor 110 and the signaltransmission structure, the additional layer extends only within theregion of the sensor 110 (e.g. not extending through boundary 102 to thesignal transmission structure 120).

Those skilled in the art will readily appreciate that variousmodifications and changes can be applied to the embodiments of theinvention as hereinbefore described without departing from tic scopedefined in and by the appended claims.

The invention claimed is:
 1. A sensor unit for use in measurements on asubject, the sensor unit comprising: a near field electromagnetic sensorcomprising a sensing surface, being a surface of an electricallyconductive layer, by which the sensor unit faces a region of interest ofthe subject, said sensing surface comprising a plurality of spaced-apartapertures defining an array of spaced-apart sensor cells, wherein eachsensor cell has a sensing region surrounded by said electricallyconductive layer; and a flexible signal transmission structure integralwith said near field electromagnetic sensor in a co-planar configurationsuch that the signal transmission structure and the near fieldelectromagnetic sensor have at least one common continuous surface, saidflexible signal transmission structure comprising a first signal layerincluding an array of conductive signal connection lines associated withsaid sensor cells and a second electrically conductive layerelectrically coupled to said electrically conductive layer of thesensing surface; wherein the signal transmission structure and the nearfield electromagnetic sensor are configured for providing impedancecontrolled signal transmission to and from the sensing regions.
 2. Thesensor unit of claim 1, wherein each of at least some of said sensorcells comprises an inner conductor element coupled to inside of therespective sensing region and electrically coupled to the respective oneof said signal connection lines.
 3. The sensor unit of claim 2, whereinat least some of the sensor cells are configured as a resistive typesensor, each of said resistive type sensors comprises the innerconductor element thereof electrically insulated from the surroundingelectrically conductive material.
 4. The sensor unit of claim 3, whereinthe resistive type sensor cell comprises an electrical insulatormaterial covering the sensing region insulating said sensor cell fromthe subject.
 5. The sensor unit of claim 3, wherein the resistive typesensor cell is configured to perform measurement, while the innerconductor element and the surrounding electrically conductive materialare brought in direct contact with the subject.
 6. The sensor unit ofclaim 2, wherein at least some of the sensor cells are configured asinductive type sensors, the inner conductor element of each of theinductive type sensing cells being connected to the electricallyconductive material surrounding the respective sensing region.
 7. Thesensor unit of claim 1, wherein said flexible signal transmittingstructure has at least one flexible band configured for bending withrespect to the sensor with a radius of curvature smaller than acharacteristic dimension of said sensor.
 8. The sensor unit of claim 1,wherein the near field electromagnetic sensor comprises: a first sensorlayer comprising a plurality of signal lines, which are electricallycoupled to said signal connection lines of the signal transmissionstructure and which are thus associated with the corresponding sensorcells; and a second sensor layer comprising said electrically conductivematerial and defining said sensing surface, said second sensor layerbeing electrically coupled to the second electrically conductive layerof the signal transmission structure.
 9. The sensor unit of claim 2,wherein the near field electromagnetic sensor comprises: a first sensorlayer comprising a plurality of signal lines, which are electricallycoupled to said signal connection lines of the signal transmissionstructure and to the inner conductor elements of the sensor cells; and asecond sensor layer comprising said electrically conductive material anddefining said sensing surface, said second sensor layer beingelectrically coupled to the second electrically conductive layer of thesignal transmission structure.
 10. The sensor unit of claim 8, whereinat least some of the signal lines are associated with the respectivesensing regions and extend in said first sensor layer along respectivepaths, a projection of each of said paths onto said sensing surfacebeing outside all other sensing regions.
 11. The sensor unit of claim 9,wherein at least some of the signal lines are associated with therespective sensing regions and extend in said first sensor layer alongrespective paths, a projection of each of said paths onto said sensingsurface being outside all other sensing regions.
 12. The sensor unit ofclaim 8, wherein at least some of the signal lines are associated withthe respective sensing regions and extend in said first sensor layeralong respective paths, a projection of each of said paths onto saidsensing surface intersecting with one or more of the other sensingregions.
 13. The sensor unit of claim 10, wherein said near fieldelectromagnetic sensor comprises an additional electrically conductivesensor layer located in between said first and second sensor layers;said additional conductive sensor layer having spaced apart signaltransmission regions configured as substantially non-conductive regionsaligned with at least some of the sensing regions, said signaltransmission regions being substantially smaller than the correspondingsensing regions, thereby providing by said additional conductive sensorlayer an electrical screening of at least a portion of the signal linesfrom the sensing regions.
 14. The sensor unit of claim 12, wherein saidnear field electromagnetic sensor comprises an additional electricallyconductive sensor layer located in between said first and second sensorlayers; said additional conductive sensor layer having spaced apartsignal transmission regions configured as substantially non-conductiveregions aligned with at least some of the sensing regions, said signaltransmission regions being substantially smaller than the correspondingsensing regions, thereby providing by said additional conductive sensorlayer an electrical screening of at least a portion of the signal linesfrom the sensing regions.
 15. The sensor unit of claim 13, wherein saidadditional conductive sensor layer is configured to provide electricalscreening of the signal lines extending along paths the projections ofwhich onto said sensing surface intersect one or more of the sensingregions.
 16. The sensor unit of claim 14, wherein said additionalconductive sensor layer is configured to provide electrical screening ofthe signal lines extending along paths the projections of which ontosaid sensing surface intersect one or more of the sensing regions. 17.The sensor unit of claim 8, wherein said second sensor layer is integralwith said second electrically conductive layer of the signaltransmission structure.
 18. The sensor unit of claim 9, wherein saidsecond sensor layer is integral with said second electrically conductivelayer of the signal transmission structure.
 19. The sensor unit of claim13, wherein said additional conductive sensor layer is integral withsaid second electrically conductive layer of the signal transmissionstructure.
 20. The sensor unit of claim 14, wherein said additionalconductive sensor layer is integral with said second electricallyconductive layer of the signal transmission structure.
 21. The sensorunit of claim 15, wherein said additional conductive sensor layer isintegral with said second electrically conductive layer of the signaltransmission structure.
 22. The sensor unit of claim 16, wherein saidadditional conductive sensor layer is integral with said secondelectrically conductive layer of the signal transmission structure. 23.The sensor unit of claim 8, wherein said first sensor layer comprisingsaid signal lines is integral with said first layer of the signaltransmission structure comprising said signal connection lines.
 24. Thesensor unit of claim 8, wherein at least some of the signal lines of thefirst sensor layer terminate within at least some of said sensingregions associated therewith; said signal lines being connected, attheir termination within the sensing regions, with the inner conductorelement protruding from said first sensor layer towards the sensingsurface, such that said electrically conductor elements induceelectromagnetic field profile extending outwards from the sensingsurface through said sensing regions.
 25. The sensor unit of claim 1,wherein said signal transmission structure comprises one or moreflexible bands capable of bending with respect to the sensor andcontaining the signal connection lines, said one or more bands extendingfrom the sensor along one or more directions.
 26. The sensor unit ofclaim 1, wherein at least one of the sensor cells is configured andoperable as a reference cell which is substantially insensitive toeffects of a region of interest of the subject to which the sensor iscoupled during operation.
 27. The sensor unit of claim 1, wherein saidsignal transmission structure is configured as a flexible planarmicrostrip having a plurality of layers including said first and secondlayers being flexible planar layers.
 28. The sensor unit of claim 1,wherein said signal transmission structure is configured as a flexibleplanar strip comprising a plurality of layers including the first andsecond layers, and additional electrically conductive layer, the secondand the additional layers being located at both sides of said firstlayer.
 29. The sensor unit of claim 1, wherein said sensing surface ofthe near field electromagnetic sensor is flexible.
 30. A sensor unit foruse in measurements on a subject, the sensor unit comprising: a nearfield electromagnetic sensor comprising a sensing surface, of anelectrically conductive layer, by which the sensor unit faces a regionof interest of the subject, said sensing surface comprising a pluralityof apertures defining an array of spaced-apart sensor cells, each sensorcell has a sensing region surrounded by said electrically conductivelayer; and a flexible signal transmission structure integral with saidnear field electromagnetic sensor in a co-planar configuration such thatthe signal transmission structure and the near field electromagneticsensor have at least one common continuous surface, said flexible signaltransmitting structure having at least one flexible band configured forbending with respect to the sensor with a radius of curvature smallerthan a characteristic dimension of said sensor; wherein the signaltransmission structure and the near field electromagnetic sensor areconfigured for providing impedance controlled signal transmission alongto and from the sensing regions.
 31. A sensor unit for use inmeasurements on a subject, the sensor unit comprising: a near fieldelectromagnetic sensor comprising an array of sensor cells eachcomprising a sensing region and an inner conductor element locatedwithin said sensing region, the sensing regions of the sensor cellsbeing arranged in a spaced-apart relationship within a sensing surface,said sensing surface being a surface of an electrically conductive layerhaving a plurality of apertures defining the array of the sensingregions in spaced-apart relationship within said sensing surface, eachsensing region being surrounded by an electrically conductive materialof said conductive layer; and a flexible signal transmission structureintegral with said near field electromagnetic sensor, said flexiblesignal transmission structure comprising a first layer including signalconnection lines electrically coupled to the inner conductor elementsrespectively; wherein the flexible signal transmission structure and thenear field electromagnetic sensor are configured for providing impedancecontrolled signal transmission along to and from the sensing regions.32. A sensor unit for use in measurements on a subject, the sensor unitcomprising: a near field electromagnetic sensor comprising a sensingsurface, of an electrically conductive layer, by which the sensor unitfaces a region of interest of the subject, said sensing surfacecomprising a plurality of apertures defining an array of spaced-apartsensor cells, each sensor cell has a sensing region surrounded by saidelectrically conductive layer and comprising an inner conductor elementcoupled to the inside of the sensing region; and a flexible microstripwhich is integral with said near field electromagnetic sensor in aco-planar configuration such that the flexible microstrip and the nearfield electromagnetic sensor have at least one common continuoussurface, said flexible microstrip being capable of bending with respectto the sensor, said flexible microstrip comprising a first conductivelayer being an extension of said electrically conductive layer of saidsensing surface and a second conductive layer carrying an array ofsignal connection lines electrically coupled to said inner conductorelements; wherein the flexible microstrip and the near fieldelectromagnetic sensor are configured for providing impedance controlledsignal transmission along to and from the sensing regions.
 33. A sensingdevice comprising one or more of the sensor units of claim
 1. 34. Ameasurement device for use in measurements on a subject, the measurementdevice comprising: a sensing device of claim 33, and a calibration andprobe control unit (CPC) which is integral with said sensing device andwhich is configured for connecting to a network analyzer.
 35. Themeasurement device of claim 34, wherein the CPC comprises a number ofterminals associated with a plurality of calibration loads of known RFreflection coefficients respectively and comprises a memory utilitycarrying recorded data indicative of the RF reflection coefficients andrecorded data indicative of RF transfer coefficients of the CPC unit,thereby enabling calculation of the RF response of each of the sensorcells within the sensing surface of the sensor unit, while remaining thesensor unit integral with CPC unit.